1. Field of the Invention
Fluorescence microscopy is now an indispensable part of modern life sciences.
The essential limitation of fluorescence microscopy resides in its limited spatial resolution that is traditionally specified by the Abbe limit and lies at approximately 200 nm in the lateral direction.
2. Prior Art
Improving the spatial resolution of optical microscopy has long been the goal of many papers. The following approaches, inter alia, have been proposed:                4Pi Microscopy [S. W. Hell and H. K. Stelzer, J. Opt. Soc. Am. A 9, 2159 (1992)], in which two objects are used to focus oppositely directed excitation beams onto a sample.        InM Microscopy which operates with spatially modulated light excitation [M. G. L. Gustafsson, J. Microsc. 198, 82 (2000)].        One multiphoton excitation [W. Denk, J. H. Strickler and W. W. Webb, Science 248, 73 (1990)].        RESOLFT, which uses nonlinear saturation effects [S. W. Hell, M. Dyba and S. Jakobs, Curr. Opin. Neurobiol. 14, 1 (2004)].        STED (stimulated emission depletion) [S. W. Hell, in: Topics in Fluorescence Spectroscopy, 5th Edn., Edited by J. R. Lakowicz (Plenum Press, New York, 1997) pages 361-422].An overview is to be found in [M. G. L. Gustafsson, Curr. Opin. Struct. Biol. 9, 627 (1999)].        